Organocatalytic strategy to telechelic oligo(ε-caprolactone-co-p-dioxanone): Photocurable macromonomers for polyester networks

Abstract

We have designed photocurable, telechelic macromonomers consisting of random oligo(ε-caprolactone-co-p-dioxanone), oligo(CL-co-DX), and demonstrated their suitability for preparing pliable polyester networks whose properties resemble those of gels.A versatile and effective metal-free co-oligomerization, catalyzed by diphenyl phosphate, was developed in bulk and at room temperature. A high rate of conversion of monomers was achieved and oligo(CL-co-DX)s with different composition and topology were obtained with controlled molar mass, approx. 2000 g mol−1, low dispersity and a random distribution of the two monomeric units. Kinetics analysis of the reaction disclosed a faster incorporation rate for the p-dioxanone (DX) than ε-caprolactone (CL). The extrapolated rate constant, kDX, was 0.030 min−1 against a kCL of 0.013 min−1. The reactivity ratios were respectively 2.7 (rDX) and 0.28 (rCL). A detailed NMR analysis was performed to elucidate the structure of the co-oligomers, which could be precisely controlled by varying the monomer feed ratio and initiator. Depending on the composition, amorphous to semicrystalline oligomers with melting points close to room temperature were obtained, which after acrylation of the chain-end gave polyester networks with high swelling capacity up to 700%, and water uptake up to 70%.